1. Field of the Invention
The present invention broadly relates to an antenna. More particularly, the present invention relates to an antenna having a band rejection filter.
2. Description of the Related Art
Existing ultra wide band (UWB) antennas focus on realizing a UWB pass band between 3.1 GHz and 10.6 GHz. However, a technique for developing antennas removing a specific frequency band while keeping a performance of the UWB pass band is required to improve communication performance.
FIG. 1 is illustrates a flat type UWB antenna having a conventional frequency notch function. The contents of the UWB antenna having a conventional frequency notch function is disclosed in Korean Patent No. 2003-0101708, incorporated herein by reference, and will be described as a conventional technique for realizing an antenna having a frequency band rejection function, as shown in FIG. 1. The above-mentioned technique suggests a method of inserting a V-shaped slot 10 into an antenna in a direction interrupting a flow of a current, thereby realizing a specific frequency band rejection function. In other words, the above-mentioned technique adopts a method of adjusting a cut-off frequency depending on a length 20 of the V-shaped slot 10. A global positioning system satellite transmits a GPS band frequency (L2 band: 1227.6 MHz, L1 band: 1575.42 MHz), and a GPS receiver also transmits the GPS band frequency. A cut-off frequency must be adjusted to be less than or equal to a pass band to cut off such a GPS band frequency in a UWB communication system using a pass band between 3.1 GHz and 10.6 GHz.
However, when the cut-off frequency is adjusted to be less or equal to the pass band using the technique disclosed in Korean Patent No. 2003-0101708 and shown in FIG. 1, the length 20 of the V-shaped slot 10 becomes too long. In other words, when the cut-off frequency is less than or equal to the pass band, the length 20 of the V-shaped slot 10 reaches 5.5 cm.
FIG. 2 illustrates a UWB antenna having a conventional frequency selectivity. The UWB antenna shown in FIG. 2 is disclosed in U.S. Patent Publication No.: 2003/0090436A1, incorporated herein by reference. In the UWB antenna, a notch 50 is formed in a substrate type analogue, thereby realizing a frequency cut-off function. However, in a case where a frequency less than or equal to a pass band is cut off using this method, a length 70 of a loop becomes too long. In a case of a UWB antenna requiring a GPS signal notch function, the length 70 of the loop reaches 11 cm.